Open air optical channel

ABSTRACT

Various embodiments of apparatus and various embodiments of methods to communicate between a first circuit board and a second circuit board using one or more open air communication channels are provided. A plurality of light transmitters and light receivers are attached to a first circuit board; and a corresponding plurality of light receivers and light transmitters are attached to a second circuit board. The light receivers on both circuit boards are disposed to receive data transmitted by the corresponding light transmitters on each circuit board. In one embodiment, where the light transmitters are laser diodes, different colors may be used to increase adjacent signal rejection. In another embodiment, the light transmitters may be laser, radio, microwave, digital, ultraviolet, or infrared light transmitters. The light transmitters may transmit data across open spaces between circuit boards, including through apertures in boards placed between the light transmitter and light receiver.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This Application is a Continuation of application Ser. No.09/822,970, filed Mar. 29, 2001.

FIELD OF THE INVENTION

[0002] The field of the invention relates to circuit boards generally,and more particularly, to apparatus and methods for communicating dataover an open space between circuit boards.

BACKGROUND OF THE INVENTION

[0003] Computers and other electrical devices operate using printedcircuit boards (PCB's), thin substrates on which chips or otherelectronic components are mounted. In the context of personal computers(PC's), some circuit boards, called backplanes, contain sockets forexpansion cards, special circuit boards that, when inserted into thebackplane, add new capabilities to the computer.

[0004] Backplanes are often described as active or passive. Activebackplanes contain logical circuitry that performs computing functions.On the other hand, passive backplanes contain almost no computingcircuitry. Most backplanes used in personal computers are active, butthere has been a recent move toward passive backplanes.

[0005] In a passive backplane system, active components such as the CPUare inserted on an additional card, making it easier to upgrade and torepair faulty components. Whether a backplane is active or passive, aPCB inserted into an expansion slot can communicate with another PCBinserted in the backplane via the PCB's edge connector, a tabbed edge ofthe PCB containing a plurality of parallel traces. When inserted into anexpansion slot, the traces on the edge connector connect with acorresponding plurality of traces inside the expansion slot. Theseinternal traces connect through the backplane to other expansion slotsand to other components on the backplane itself. In this manner, thebackplane's internal bus architecture can be used to communicate datafrom one PCB to another PCB located further down the backplane.

[0006] Though effective, the internal bus approach is problematic.First, the large number of required traces and connectors quicklyconsumes available board space. Second, though the rate of data transferis theoretically only limited by the clock speed of the bus, bottlenecksoften cripple the rate of data transfer and impair communication betweencircuit boards. Third, inserting or removing a circuit board duringoperation of the computer or electronic device is almost unthinkable. Atthe very least, doing so may cause a minor data loss. At worst, a systemcrash may result. Consequently, it is difficult to diagnose, repair,and/or replace faulty expansion cards without first shutting down theentire system. Fourth, communication channels are only established whenthe expansion cards are properly seated within the expansion slots.Fifth, signal quality may be at risk if specific engineering guide linesare not followed such stripline or Micro-Strip. Gaps in datatransmission may occur if the card is removed or is not properly seated.

[0007]FIG. 1 illustrates a common circuit board 100, which consists ofchips 102, traces 103 and other components (104, 105) attached to asingle or multi-layer substrate. Traces 103 terminate at edge connector106, which is the part of the circuit board that is inserted into anexpansion slot in a backplane. Though most expansion cards use coppertraces, there has been a recent move towards replacing the copper traceswith a single optical fiber. Wave division multiplexing gives a singleoptical fiber tremendous bandwidth, but optical fiber suffers from thesame problems affecting copper traces. For example, PCB's using opticalfiber must be properly seated within an expansion slot to work properly,and should not be inserted or removed without first shutting down theentire system.

[0008] Today's high availability systems operate continuously around theclock. Consequently, new developments in fault-tolerant technology arerequired. Such developments should virtually eliminate the need tophysically connect PCB's with copper traces or optical fiber, and shouldenable expansion cards to be removed or added to a system's backplanewithout disrupting system operation.

[0009] As will be evident from the figures and accompanying writtendescriptions, the open air communication channel embodied by the presentinvention supplies solutions to these and other needs long felt in theart.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings, in which

[0011]FIG. 1 illustrates a prior art circuit board;

[0012]FIG. 2 illustrates two circuit boards having multiple open aircommunications channels between them according to one embodiment of theinvention;

[0013]FIG. 3 illustrates two circuit boards inserted into a backplanethat have multiple open air communications channels between themaccording to another embodiment of the invention;

[0014]FIG. 4 illustrates a fault tolerant backplane according to anotherembodiment of the invention;

[0015]FIG. 5a illustrates a stack of eight circuit boards according toanother embodiment of the invention;

[0016]FIG. 5b illustrates a sectional end view of the stack of circuitboards shown in FIG. 5a; and

[0017]FIG. 6 illustrates a sectional view of a stack of circuit boardshaving multiple open air communications channels between them accordingto another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0018] Various embodiments of apparatus and various embodiments ofmethods to communicate between a first circuit board and a secondcircuit board using one or more open air communications channels aredisclosed. In the following detailed description, numerous specificdetails are set forth in order to provide a thorough understanding ofthe present invention. However, it will be apparent to one of ordinaryskill in the art that these specific details need not be used topractice the present invention. In other circumstances, well-knownstructures, materials, or processes have not been shown or described indetail in order not to unnecessarily obscure the present invention.

[0019] Referring now to FIG. 2, two circuit boards (201, 202) are shown,according to one embodiment of the invention, having multiple open aircommunications channels (230, 240) between them. Each circuit board(201, 202) includes one or more light transmitters (210, 220) and one ormore corresponding light receivers (212, 222). In one embodiment, lightreceivers 212 and 222 are uniquely tuned to the transmitting frequenciesof corresponding light transmitters 210 and 220. As used herein, theterm “light” includes visible and invisible light. For example, a lighttransmitter may transmit data signals using visible or invisible light.

[0020] In one embodiment, Vertical Cavity Surface Emitting Lasers(VCSELs) are used as light transmitters (210, 220). Because it isdesirable to improve the signal integrity of each communication channel(230, 240) by maximizing each channel's signal-to-noise ratio (SNR), theplacement of the VCSELs needs to have proper spacing so that the samecolor VCSEL does not interfere with an unintended neighboring lightreceiver of the same frequency color. Additionally, an appropriatecalumniating lens system may be used to attenuate the transmission beam.By picking colors appropriately, wider columns of transmission beams canbe used that will ease communication and alignment with targeted lightreceivers. In another embodiment, controlled doping on VCSEL arrays maybe used to ease constriction of light channel matrix construction.

[0021] Using one or more communication channels between printed circuitboards (PCBs) eliminates the copper traces on the edge connectors, andachieves data transfer rates that exceed the rates achieved bytraditional backplane systems now in use. For example, in traditionalbackplane systems, impedance in the copper traces lowers the SNR of thetransmission path, considerably slowing data transfer rates from what istheoretically possible. By sidestepping the copper backplanearchitecture altogether, embodiments of the present invention minimizeor eliminate the copper trace impedance that formerly lowered the SNR ofthe transmission path. Consequently, the SNR of the transmission path israised, and data transfer rates are increased.

[0022] Referring now to FIG. 3, two circuit boards (301, 302) are shownremovably inserted into a backplane 306, which may be attached to achassis 303 as shown. A plurality of light transmitters (310, 320, 330)and a corresponding plurality of light receivers (312, 322, 332) may becoupled with one or both sides of circuit boards (301, 302) in a varietyof combinations.

[0023] In one embodiment, one or more light transmitters may be attachedto only one side of each of circuit boards 301 and 302. In anotherembodiment, one or more light receivers may be attached to only one sideof each of circuit boards 301 and 302. In yet another embodiment, afirst side of each of circuit boards 301 and 302 may contain one or morelight transmitters, while the other side contains one or more lightreceivers. In other embodiments, one or both sides of each of circuitboards 301 and 302 may contain one or more light transmitters and lightreceivers. In any embodiment, the light receivers and light transmittersmay be placed anywhere within the X-Y plane of the circuit board towhich they are attached, including the planar surface of the circuitboard's tabbed edge connector. Additionally, one or more lighttransmitters and/or light receivers may be positioned within thethickness of an edge or edges of the circuit board substrate. Edgemounting light receivers and/or light transmitters on circuit board 301or 302 expands the number of communication channels available. Forexample, whereas a circuit board having light receivers and lighttransmitters coupled with both of its planar surfaces can communicateonly with two other adjacent boards, a circuit board having edge mountedlight receivers and light transmitters can communicate with at leastfour other circuit boards positioned around its four edges.

[0024] Light transmitters and/or light receivers may be attached to orcoupled with a circuit board using any one of a number of suitableattachment or coupling methods well known in the art, such as, forexample, by soldering, by an adhesive, or by a physical connection, suchas a bracket. In one embodiment, the light receivers and/or lighttransmitters may be flush mounted within apertures in the circuit board.In another embodiment, brackets 321 may be used to attach the lighttransmitters and/or light receivers to the circuit board.

[0025] Optical fiber may be used to link light transmitters and/or lightreceivers to a circuit board where it is desirable to connect them tovarious components on the circuit board, such as other lighttransmitters and/or light receivers. For example, in FIG. 3, an opticalfiber (not shown) may be used to link light receiver 312 on one side ofcircuit board 302 with light transmitter 315 on the other side ofcircuit board 302. Where it is desirable to increase the bandwidth ofthe circuit board's internal bus architecture, the copper traces runningbetween the card's components may be supplemented or replaced withoptical fibers capable of handling 1,024 or more colors (communicationchannels).

[0026] In one embodiment, the elements needed to construct acommunication channel include, but are not limited to: (i) a lighttransmitter (ii) in communication with a corresponding light receiver(iii) over or through an open space between the light transmitter andits corresponding light receiver. When constructing a communicationchannel, care should be taken to prevent contaminants such as dust orsmoke from filtering through the open spaces between light transmittersand light receivers; otherwise, the integrity and reliability of thecommunication channel may be compromised.

[0027] As shown in FIG. 3, a light channel 305 may be formed withinbackplane 306 to prevent ambient light and other contaminants fromdisrupting communication channel 360. In one embodiment, light channel305 may be an enclosed optical space bounded on at least one side by thestructural material of backplane 306 (and/or expansion slot 304). Inanother embodiment, multiple communication channels may be formed withinlight channel 305.

[0028] It may be desirable to reduce or eliminate cross-overinterference in embodiments where light receivers are placed adjacenteach other or in close proximity to each other. Transmission beams tendto expand radially outward over distance. In some embodiments, suchexpansion may cause a transmission beam to overlap light receiversadjacent or in close proximity to the target light receiver, resultingin interference with signals in other communication channels. In oneembodiment, cross-over interference can be reduced or substantiallyeliminated by assigning each light transmitter and corresponding lightreceiver a particular color or broadcast frequency. For example, lighttransmitter 310 in FIG. 3 may be a blue laser, while light transmitter320 may be a red laser. Such an embodiment reduces cross-overinterference and increases adjacent signal rejection because lightreceiver 322, being tuned to receive red laser light, will reject anyblue laser light that happens to overlap it. Other methods of increasingadjacent signal rejection include, but are not limited to: increasingthe spacing between light receivers, attenuating the transmission beamusing appropriate lenses and/or doping methods, and placing differentcolor (frequency) light receivers between light receivers of the samecolor (frequency).

[0029] Referring now to FIG. 4, a fault tolerant backplane 406 is shownaccording to another embodiment of the invention. Backplane 406 includesthree expansion slots (407, 408, 409) into which three circuit boards(401, 402, 403) are respectively removably inserted. Circuit boards 401and 403 are virtually identical in appearance, with circuit board 401having light transmitters 410, 420, 430 attached to its upper surfaceand light receivers 419, 421, 431 attached to its lower surface, andcircuit board 403 having light transmitters 417, 425, 437 attached toits upper surface and light receivers 414, 422, 434 attached to itslower surface. Circuit board 402 is positioned between boards 401 and403. Light transmitters 415 and 435 are attached to is upper surface,and light receivers 412, 432 are attached to its lower surface. Circuitboard 402 contains an aperture 405, which enables board 401 to “see”board 403.

[0030] Communication channel 440 is formed between light transmitter 410on board 401 and corresponding light receiver 412 on board 402.Communication channel 441 is formed between light transmitter 415 onboard 402 and light receiver 414 on board 403. Communication channel 450is formed between light transmitter 420 on board 301 and correspondinglight receiver 422 on board 403 via aperture 405 in board 402 thatallows transmission beam 450 to pass unimpeded through circuit board402. The last two communications channels 460 and 461 are formed withinthe structure of backplane 406 and may be used to power or groundcircuit boards (401, 402, 403). Channel 460 is formed between lighttransmitter 430 on board 401 and light receiver 432 on board 402.Channel 461 is formed between light transmitter 435 on board 402 andlight receiver 434 on board 403.

[0031] Backplane 406 in FIG. 4 is fault-tolerant and self-healing. Forexample, if board 402 is removed from backplane 406, communicationbetween light transmitter 410 and light receiver 414, between lighttransmitter 420 and light receiver 422, and between light transmitter430 and light receiver 434 will be automatically reestablished atvarious times as board 402 is removed. For example, channels 460 and 461will be the first to merge, followed by a brief merger of channels 440and 441 as aperture 405 passes between light transmitter 410 and lightreceiver 414, followed by the reacquisition of channel 450, followed bya final merging of channels 440 and 441.

[0032] Each board can be programmed to automatically retry establishingan operable communication channel whenever a change in signal generationis detected. Alternatively, each board can be programmed toautomatically reroute data traffic from an inoperable communicationchannel to an operable one whenever an absence of data signal (in oneembodiment, light) is detected.

[0033] Contrast the self healing aspect of the present invention withthe non-self-healing aspect of circuit boards using copper traces oroptical fiber. In these types of boards, removal of the copper trace oroptical fiber kills the channel, which remains dead as the faultycircuit board is removed, a new one inserted, the traces or opticalfiber reconnected, and the system is reinitialized.

[0034] In one embodiment, boards 401, 402, 403 may each have the same ordifferent functionalities. Similarly, expansion slots 407, 408, 409 mayeach have the same or different functionalities. For example, expansionslot 408 may have a specific signal the other expansion slots do not. Inone embodiment, a board's functionality is “slot independent”, meaningthat the functionality resides entirely within the board. In anotherembodiment, each card's functionality is determined by the expansionslot in which it is removably inserted (slot dependent functionality).In one slot dependent embodiment having eight expansion slots, two maybe used as controllers, and the remaining six divided as needed betweeninput/output and storage functions (e.g. four input/output and twostorage).

[0035] Referring now to FIGS. 5a and 5 b, FIG. 5a shows a perspectiveview of a stack of eight circuit boards according to one aspect of theinvention. FIG. 5b illustrates a sectional end view of the stack ofeight circuit boards shown in FIG. 5a.

[0036] In FIG. 5a, a stack of eight circuit boards is shown. The boardsare consecutively numbered 1-8, with board 1 on the bottom of the stack,and board 8 on the top. One edge of each board includes one or more tabsthat may be inserted into the expansion slot(s) of a backplane. The tabsare consecutively numbered 501-508 to correspond with the appropriateboard. For example, board 1 includes tabs 501; board 2 includes tabs502, board 3 includes tabs 503, and so on.

[0037] The tabs on each board occupy one or more of five columnarpositions. In FIG. 5b, the columnar positions are represented by columns511, 512, 513, 514, and 515, which are numbered consecutively from leftto right. The tabs are represented in FIG. 5b as shaded rectangles. Eachrectangle representing a tab is shaded the same as the board to which itis attached. For example, tabs 501 in FIG. 5a are represented in FIG. 5bas diagonally shaded rectangles because board 1 in FIG. 5a is diagonallyshaded. Additionally, the stack of boards in FIG. 5b is numberedconsecutively 1-8 on both sides, beginning with board 1 on the bottomand ending with board 8 on the top.

[0038] Careful arrangement of tabs 501-508 enables various pairs ofboards located on different levels of the stack to communicate with eachother. For example, tabs 501 and 505 occupy both columnar position 511and columnar position 513. The absence of tabs in column 511 on boards2, 3, and 4 allows a light transmitter (not shown) attached to the topside of tab 501 to communicate with a corresponding light transmitter(not shown) attached to the bottom side of tab 505. In this manner,communication channel 520 may be established in columnar position 511between boards 1 and 5. Similarly, board 2 may communicate directly withboard 8 using communication channel 530 in columnar position 512; board3 may communicate directly with board 6 using communication channel 550in columnar position 514; and board 4 may communicate directly withboard 7 using communication channel 560 in columnar position 515.Communication channel 540, in columnar position 513 may be used to relaya power signal from board to board.

[0039] Communication channel 540 is fault tolerant and self-healing inthat removal of an interior board simply connects the relayedsupervisory signal to the next available board. For example, if board 3were removed, the supervisory signal from board 2 would be automaticallyrelayed to board 4. In one embodiment, the supervisory signal enablesthe system to recognize the presence or absence of a board.

[0040] The other communication channels are also self-healing in thatremoval of an interior board will not disrupt communications. Forexample, board 3 may be removed without disrupting communicationchannels 520 or 530 because board 3 has no tabs in columnar positions511 or 512. However, removal of board 3 would disrupt communicationchannel 550 because tab 503 occupies columnar position 514 and may carrya light transmitter and/or light receiver.

[0041] Each of boards 1-8 may be equipped with notification circuitrydesigned to (i) detect a change in transmission intensity (e.g. such asthat caused by the removal or fault of a light transmitter and/or lightreceiver), to (ii) automatically shutdown the affected communicationchannel, and (iii) to automatically reroute data traffic to anotheroperable channel, and/or (iv) to automatically retry to establishcommunications in the affected channel(s).

[0042] Referring now to FIG. 6, a sectional end view of a stack of eighttabbed circuit boards is shown according to another embodiment of theinvention. The boards in the stack are consecutively numbered 1-8,beginning with board 1 on the bottom, and ending with board 8 on thetop. In this embodiment, one edge of each circuit board has one or moretabs that may be inserted within the expansion slots of a backplane (notshown). The tabs are consecutively numbered 601-608 to correspond to thecircuit board to which they are attached. For example, tab 601 isattached to board 1; tab 602 to board 2; tab 603 to board 3, and so on.

[0043] The tabbed portions of each circuit board may occupy one or moreof three columnar positions 611, 612, 613. In FIG. 6, these tabbedportions are represented by shaded rectangular blocks. For example, tabs608 are represented by blocks filled with cross-hatched shading; tab 607is represented by a block filled with uniform grey shading, and so on.

[0044] In FIG. 6, tabs 601-608 are arranged within columns 601, 602, 603to allow communications between pairs of boards located on differentlevels within the stack. For example, light transmitters 622 on the topsurface of tab 601 can communicate with light receivers 624 on thebottom surface of tab 605. Similarly, light transmitters 623 on thebottom surface of tab 605 can communicate with light receivers 621 onthe top surface of tab 601.

[0045] In this manner, a plurality of communication channels 610, 620,630, 640, may be established between tabs 601 and 605. Similarpluralities of communication channels may be formed between tabs incolumns 612 and 613. The two communication channels 650 and 660 formedin column 613 may be used to relay a power signal from board to board.Additionally, the communication channels shown in FIG. 6 arefault-tolerant and self-healing in the same way as the channelsillustratively described with reference to FIG. 5b.

[0046] Thus, apparatus and methods to communicate between a firstcircuit board and a second circuit board using one or more open aircommunications channels are disclosed. Although the present invention isdescribed herein with reference to a specific preferred embodiment, manymodifications and variations therein will readily occur to those withordinary skill in the art. Accordingly, all such variations andmodifications are included within the intended scope of the presentinvention as defined by the following claims.

What is claimed is:
 1. An apparatus, comprising: a first lighttransmitter disposed on a first circuit board to communicate using afirst frequency through air with a first light receiver disposed on asecond circuit board, the first and the second circuit boards beingdisposed in a backplane; and a second light transmitter disposed on thefirst circuit board to communicate using a second frequency through airwith a second light receiver disposed on the second circuit board, thefirst light receiver to reject the second frequency, the second lightreceiver to reject the first frequency.
 2. The apparatus of claim 1wherein the first and/or the second light transmitter is a laser diode.3. The apparatus of claim 2 wherein the laser diode is a Vertical CavitySurface Emitting Laser (VCSEL).
 4. The apparatus of claim 1 wherein thefirst light receiver is tuned to the frequency of the first lighttransmitter.
 5. The apparatus of claim 1 wherein the first and/or thesecond light transmitter is selected from the group consisting of alaser transmitter, a radio transmitter, a digital transmitter, aninfrared transmitter, and an ultraviolet transmitter.
 6. The apparatusof claim 1, further comprising; a first fiber optic cable is operativelycoupled with the first light transmitter to relay data signals to thefirst light transmitter; and a second fiber optic cable operativelycoupled with the second light receiver to relay data signals received bythe second light receiver.
 7. The apparatus of claim 1 wherein the firstand the second light transmitters and the first and the second lightreceivers are housed within a card or system chassis.
 8. A method,comprising: transmitting a first data signal on a first light signalhaving a first color from a first laser diode disposed on a firstcircuit board to a first target light receiver disposed on a secondcircuit board, the first target light receiver being tuned to the firstcolor, the first and the second circuit boards being disposed in abackplane; and transmitting a second data signal on a second lightsignal having a second color from a second laser diode disposed on thefirst circuit board to a second target light receiver disposed on thesecond circuit board, the second target light receiver being tuned tothe second color.
 9. The method of claim 8, further comprising rejectingthe first frequency using the second light receiver.
 10. The method ofclaim 9, further comprising rejecting the second frequency using thefirst light receiver.